In the dry mortar industry, cellulose ethers are typically used as water retention agents to achieve good water retention of the resulting wet mortar. Water retention is needed to control the water content for proper hydration of the mortar, including any binder, and to achieve good workability of the mortar. Secondary beneficial effects resulting from correct hydration performance of the mortar are proper strength development of the mortar and avoidance of cracks and sanding effects of the applied mortar layer.
Typical cellulose ethers used for dry mortar application are methyl hydroxyethyl cellulose (MHEC) and methyl hydroxypropyl cellulose (MHPC). Mortars containing MHEC and/or MHPC exhibit the desired properties of strength development, avoidance of cracks and sanding effects. Unfortunately, MHEC and MHPC typically do not afford mortars with hot temperature stability. Due to their hydrophobic character, they either do not properly dissolve at elevated temperatures or they precipitate and consequently become inactive upon temperature increase in the mortar.
Because of its hydrophilic nature, hydroxyethyl cellulose (HEC) does not precipitate in aqueous solutions in response to increased temperature and is capable of providing temperature stability to wet mortar, even at very high temperatures. Unfortunately, HEC does not provide sufficient air void stabilization in the resulting mortar, i.e. mortars containing HEC. In mortars containing standard HEC, the mortars exhibit small air bubbles which then coagulate into larger bubbles within the wet mortar. The resultant applied mortar containing standard HEC exhibits a bad and mostly unacceptable surface appearance due to the presence of these large bubbles in the mortar.
The need exists for a mortar which has the necessary pot life and open time under hot weather conditions to permit the application of the mortar while retaining enough water during mixing and upon application to result in a finished surface with the necessary functionality and aesthetics.